Your motherboard i probably using some of your ram for video. Aside from that, RAM isn't an exact science so you don't get exactly what it says. All computers will list different amounts, not exactly this many MB's. When you get to GB it's a bit easier because the numbers are small.

Don't worry, it's normal. Do you have an onboard sound or videocard, this is where some of the ram might be being used up. Otherwise, it's just how your computer reads the ram.

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Hi,
this will be dependant on the bios version. or if the 2 ram modules are identical or not. if they,re a matched pair. the motherboard may not like or run in dual-channel mode. sometimes adjustable in the systems bios. the other suggestion, is to try 1 stick of ram, in each slot individually. This will eliminate A Faulty Slot. Failing any Of The Above. try 2 x 256mb sticks, And Obtain The Latest Bios Update from The Manufacturers Website.

fine ur problem if very simple as u installed 512 mb RAM on ur pc if at possible try to connect on to the other slot and restart the computer and check ur RAM capacity in ur os if it shows as same 256mb then ur have to change ur virtual memory settings i.e memory allocated to the video so configure ur virtual memory as per requirement then free up RAM memory ..

Steps for virtual memory configuration.

Open System in Control Panel.

On the Advanced tab, under Performance, click Settings.

On the Advanced tab, under Virtual memory, click Change.

Under Drive [Volume Label], click the drive that
contains the paging file you want to
change.

Under Paging file size for selected drive, click Custom size,
and type a new paging file size in megabytes in the Initial size (MB) or
Maximum size (MB) box, and then click Set.
If you decrease the size of either the initial or maximum page file settings,
you must restart your computer to see the effects of those changes. Increases
typically do not require a restart.

take the working 256 meg stick out of the slot it,s in. and try it in slot 2 or vice-versa.
This will eliminate the possibility of the mainboard being faulty.
If you get a boot on both Ram slot channels, then your Ram is dead, or incorrect. Check that it,s compatable with the motherboard. i.e running speed 2700-3200-et,c and that it is the correct parity and voltage, as per required by the board/CPU.